Deprecate java.generate_native_header() in favor of java.generate_native_headers()

After implementing a much more extensive Java native module than what
currently exists in the tests, I found shortcomings.

1. You need to be able to pass multiple Java files.
2. Meson needs more information to better track the generated native
   headers.
3. Meson wasn't tracking the header files generated from inner classes.

This new function should fix all the issues the old function had with
room to grow should more functionality need to be added. What I
implemented here in this new function is essentially what I have done in
the Heterogeneous-Memory Storage Engine's Java bindings.

5 files changed, 127 insertions, 6 deletions

diff --git a/docs/markdown/Java-module.md b/docs/markdown/Java-module.md
index 9857de7..1665b7b 100644
--- a/docs/markdown/Java-module.md
+++ b/docs/markdown/Java-module.md
@@ -1,11 +1,13 @@
 # Java Module
 
-*Added 0.60.0*
+*(added in 0.60.0)*
 
 ## Functions
 
 ### `generate_native_header()`
 
+*(deprecated in 0.62.0, use `generate_native_headers()`)*
+
 This function will generate a header file for use in Java native module
 development by reading the supplied Java file for `native` method declarations.
 
@@ -13,3 +15,46 @@ Keyword arguments:
 
 - `package`: The [package](https://en.wikipedia.org/wiki/Java_package) of the
 file. If left empty, Meson will assume that there is no package.
+
+### `generate_native_headers()`
+
+*(added in 0.62.0)*
+
+This function will generate native header files for use in Java native module
+development by reading the supplied Java files for `native` method declarations.
+
+Keyword arguments:
+
+- `classes`: The list of class names relative to the `package`, if it exists,
+which contain `native` method declarations. Use `.` separated class names.
+
+- `package`: The [package](https://en.wikipedia.org/wiki/Java_package) of the
+file. If left empty, Meson will assume that there is no package.
+
+Example:
+
+```java
+// Outer.java
+
+package com.mesonbuild;
+
+public class Outer {
+    private static native void outer();
+
+    public static class Inner {
+        private static native void inner();
+    }
+}
+```
+
+With the above file, an invocation would look like the following:
+
+```meson
+java = import('java')
+
+native_headers = java.generate_native_headers(
+    'Outer.java',
+    package: 'com.mesonbuild',
+    classes: ['Outer', 'Outer.Inner']
+)
+```
diff --git a/docs/markdown/snippets/java_generate_native_headers.md b/docs/markdown/snippets/java_generate_native_headers.md
new file mode 100644
index 0000000..2a2a89e
--- /dev/null
+++ b/docs/markdown/snippets/java_generate_native_headers.md
@@ -0,0 +1,34 @@
+## Deprecated `java.generate_native_header()` in favor of the new `java.generate_native_headers()`
+
+`java.generate_native_header()` was only useful for the most basic of
+situations. It didn't take into account that in order to generate native
+headers, you had to have all the referenced Java files. It also didn't take
+into account inner classes. Do not use this function from `0.62.0` onward.
+
+`java.generate_native_headers()` has been added as a replacement which should account for the previous function's shortcomings.
+
+```java
+// Outer.java
+
+package com.mesonbuild;
+
+public class Outer {
+    private static native void outer();
+
+    public static class Inner {
+        private static native void inner();
+    }
+}
+```
+
+With the above file, an invocation would look like the following:
+
+```meson
+java = import('java')
+
+native_headers = java.generate_native_headers(
+    'Outer.java',
+    package: 'com.mesonbuild',
+    classes: ['Outer', 'Outer.Inner']
+)
+```
diff --git a/mesonbuild/modules/java.py b/mesonbuild/modules/java.py
index 20cf3fd..dc660a7 100644
--- a/mesonbuild/modules/java.py
+++ b/mesonbuild/modules/java.py
@@ -15,9 +15,10 @@
 import os
 import pathlib
 import typing as T
+from mesonbuild import mesonlib
 from mesonbuild.build import CustomTarget
 from mesonbuild.compilers import detect_compiler_for
-from mesonbuild.interpreterbase.decorators import FeatureNew, KwargInfo, typed_pos_args, typed_kwargs
+from mesonbuild.interpreterbase.decorators import ContainerTypeInfo, FeatureDeprecated, FeatureNew, KwargInfo, typed_pos_args, typed_kwargs
 from mesonbuild.interpreter.interpreterobjects import FileHolder
 from mesonbuild.mesonlib import version_compare, MachineChoice
 from . import ExtensionModule, ModuleReturnValue, ModuleState
@@ -29,18 +30,18 @@ class JavaModule(ExtensionModule):
         super().__init__(interpreter)
         self.methods.update({
             'generate_native_header': self.generate_native_header,
+            'generate_native_headers': self.generate_native_headers,
         })
 
         if 'java' not in interpreter.environment.coredata.compilers[MachineChoice.BUILD]:
             detect_compiler_for(interpreter.environment, 'java', MachineChoice.BUILD)
         self.javac = interpreter.environment.coredata.compilers[MachineChoice.BUILD]['java']
 
+    @FeatureDeprecated('java.generate_native_header', '0.62.0', 'Use java.generate_native_headers instead')
     @typed_pos_args('generate_native_header', (str, FileHolder))
     @typed_kwargs('java.generate_native_header', KwargInfo('package', str, default=None))
     def generate_native_header(self, state: ModuleState, args: T.Tuple[T.Union[str, FileHolder]],
                                kwargs: T.Dict[str, T.Optional[str]]) -> ModuleReturnValue:
-        assert state.backend
-
         package = kwargs.get('package')
 
         file = self.interpreter.source_strings_to_files(
@@ -74,5 +75,45 @@ class JavaModule(ExtensionModule):
 
         return ModuleReturnValue(target, [target])
 
+    @FeatureNew('java.generate_native_headers', '0.62.0')
+    @typed_pos_args('generate_native_headers', (str, mesonlib.File), min_varargs=1)
+    @typed_kwargs('java.generate_native_headers',
+        KwargInfo('classes', (ContainerTypeInfo(list, str)), default=[], listify=True,
+            required=True),
+        KwargInfo('package', str, default=None))
+    def generate_native_headers(self, state: ModuleState, args: T.List[mesonlib.FileOrString],
+                               kwargs: T.Dict[str, T.Optional[str]]) -> ModuleReturnValue:
+        classes = T.cast(T.List[str], kwargs.get('classes'))
+        package = kwargs.get('package')
+
+        headers: T.List[str] = []
+        for clazz in classes:
+            underscore_clazz = clazz.replace(".", "_")
+            if package:
+                headers.append(f'{package.replace(".", "_")}_{underscore_clazz}.h')
+            else:
+                headers.append(f'{underscore_clazz}.h')
+
+        command = mesonlib.listify([
+            self.javac.exelist,
+            '-d',
+            '@PRIVATE_DIR@',
+            '-h',
+            state.subdir,
+            '@INPUT@',
+        ])
+
+        prefix = classes[0] if not package else package
+
+        target = CustomTarget(f'{prefix}-native-headers', state.subdir, state.subproject, command,
+                              sources=list(args), outputs=headers, backend=state.backend)
+
+        # It is only known that 1.8.0 won't pre-create the directory. 11 and 16
+        # do not exhibit this behavior.
+        if version_compare(self.javac.version, '1.8.0'):
+            pathlib.Path(state.backend.get_target_private_dir_abs(target)).mkdir(parents=True, exist_ok=True)
+
+        return ModuleReturnValue(target, [target])
+
 def initialize(*args: T.Any, **kwargs: T.Any) -> JavaModule:
     return JavaModule(*args, **kwargs)
diff --git a/test cases/java/9 jdk/lib/meson.build b/test cases/java/9 jdk/lib/meson.build
index edffc1c..08407cf 100644
--- a/test cases/java/9 jdk/lib/meson.build
+++ b/test cases/java/9 jdk/lib/meson.build
@@ -3,7 +3,7 @@ sources = [
     'native.c',
     'com_mesonbuild_JdkTest.c',
   ),
-  native_header
+  native_headers
 ]
 
 jdkjava = shared_module(
diff --git a/test cases/java/9 jdk/src/com/mesonbuild/meson.build b/test cases/java/9 jdk/src/com/mesonbuild/meson.build
index 07daf51..0cce7f0 100644
--- a/test cases/java/9 jdk/src/com/mesonbuild/meson.build
+++ b/test cases/java/9 jdk/src/com/mesonbuild/meson.build
@@ -1,2 +1,3 @@
-native_header = javamod.generate_native_header('JdkTest.java', package: 'com.mesonbuild')
+native_headers = javamod.generate_native_headers(
+  'JdkTest.java', package: 'com.mesonbuild', classes: ['JdkTest'])
 native_header_includes = include_directories('.')